SO2 seasonal variation and assessment of Ozone Monitoring Instrument (OMI) measurements at Sharpeville (27.86°E; 26.68°S) a South African ground-based station

ABSTRACT

In this study, seasonal, inter-annual variations of sulphur dioxide (SO₂) were analysed for Sharpeville, South Africa (27.86°E; 26.68°S) for the period 2007–2013. Sharpeville is a residential site located within a highly industrialized region. Inter-annual variations were investigated by analysis of data collated by a ground-based (GB) instrument as well as the SO₂ retrievals recorded by the Ozone Monitoring Instrument (OMI), a satellite-based sensor. The planetary boundary layer (PBL) SO₂ vertical column data recorded by OMI were converted to surface SO₂ volume mixing ratios using the pressure difference between surface and PBL. Accordingly, the OMI-derived SO₂ measurements overestimated GB values and showed a good correlation with GB data in the austral winter. Besides this, the overall comparisons i.e. their daily, seasonal, and yearly correlation studies found that OMI-derived measurements was in better agreement with GB regardless of its moderate relative percentage of difference with GB. The seasonal variations of SO₂ demonstrated that GB and OMI-derived measurements followed a general pattern of increasing trend from autumn until late winter and decreased from the onset of spring; however, the latter showed unique high SO₂ levels in summer. Together with this, the inter-annual variations of both computations displayed a small decrement in SO₂ values during the period 2011–2013. This however proved to be a stable variation when compared to other countries.

Acknowledgements

The authors would like to express their appreciation to the South African Weather Service and those in charge of the South African Air Quality Information System (SAAQIS) for providing the necessary data from the GB monitoring station. The first author (SKS) thanks the South African National Space Agency (SANSA) Earth observation for financially supporting to conduct this study. CYW receives funding support from the South African Medical Research Council and the National Research Foundation.

Disclosure statement

No potential conflict of interest was reported by the authors.